Characterization of [11C]vorozole binding in ovarian tissue in rats throughout estrous cycle in association with conversion of androgens to estrogens in vivo and in vitro

Estrogen levels vary in a cyclic fashion during the rat estrous cycle, reaching peak concentrations during proestrus. Previously, it was suggested that the preovulatory peak in estrogen production in rats in vivo is regulated by other control mechanisms than concentration of precursor and amount of aromatase enzyme, changing the specific activity of the enzyme. To explore this hypothesis, ovarian binding of [11C]vorozole in vivo and in vitro, representing the amount of active aromatase, and conversion activity of ovarian homogenate were assayed together with serum androstenedione (A4) and estradiol-17beta (E2) levels during the estrous cycle in rats. The reducing ovarian [11C]vorozole binding in vivo from proestrus +4 up to +8h might indicate that the ovarian aromatase is blocked, probably to prevent premature increase of E2 levels. Thereafter (between proestrus +9 and +13h), the binding dramatically increases (aromatase enzyme is unblocked), to enable increased E2 synthesis. In addition, during the latter period, serum E2 levels were strongly correlated with serum A4 levels after adjustment for amount of ovarian aromatase (P=0.03), but not with amount of aromatase adjusted for levels of A4 (P=0.13), which might indicate changes in specific activity of the aromatase enzyme. Significant correlation between Kd and serum E2 levels during the same period indicated that aromatase-precursor affinity might be involved in the regulation of the enzyme-specific activity. This conclusion is done assuming that [11C]vorozole binding mimics that of the substrate (A4). The [11C]vorozole in vivo technique keeps auto- and paracrine mechanisms intact, and might therefore yield additional information about biological processes compared with traditional in vitro techniques.     

A role for aromatizable androgens in female rat puberty

The function that aromatizable androgens may have in female puberty is unclear. The present experiments were undertaken to examine, using a quantitative approach, the role that physiological levels of these androgens may play in determining the timing of vaginal opening and first ovulation in female rats. Serum androstenedione (delta 4) levels increased markedly between Postnatal Days 4 and 8, remained elevated through Day 16, and declined thereafter to remain at about 100 pg/ml throughout juvenile development (Days 20-32). Serum testosterone (T) also increased, though less prominently after Postnatal Day 4. Maximal values were found at Day 12 (about 150 pg/ml); thereafter, T levels decreased to intermediate values (about 100 pg/ml), which were maintained during juvenile days. Serum dehydroepiandrosterone (DHA) remained undetectable throughout prepubertal development. At puberty, serum delta 4 increased 2.5-fold, but only at the time of the preovulatory luteinizing hormone (LH) surge. In contrast, T levels increased significantly 2-fold on the early proestrous-2 phase of puberty, 3.5-fold on the morning of first proestrus, and 9-fold at the time of the LH surge. Serum DHA remained undetectable. Implantation of Silastic capsules containing T at 2 or 6 mg/ml oil into juvenile 28-day-old rats resulted in serum T levels similar to those found on early proestrous 2 (about 150-180 pg/ml) and at 1300 h of first proestrus (ca. 300-400 pg/ml), respectively. Both treatments induced precocious vaginal opening, but failed to advance first ovulation. About 50% of the T-implanted rats had ambiguous estrous-type vaginal cytology preceding the day of first diestrus, and failed to show corpora lutea at this time.(ABSTRACT TRUNCATED AT 250 WORDS)     

A comparison of methods measuring aromatase activity in human placenta and rat ovary

The single step chromatographic product isolation method using [4-14C]-androstenedione and the tritiated water method using either [1 beta, 2 beta-3H]- or [1 beta-3H]-androstenedione have been used to determine a suitable method to measure the aromatase activity in rat ovarian 1000 g supernatant and human placental microsomes. The single step product isolation method using [4-14C]A4 reveals the presence of four distinct [4-14C]-labelled products in the rat ovary of which only the synthesis of estradiol is markedly inhibited by CGS 16949A, a well established aromatase inhibitor. In the human placenta, the formation of both [4-14C]-estrone and [4-14C]-estradiol is strongly inhibited by CGS 6949A. Therefore, in the rat ovary spurious results are obtained if accumulative radiolabelled product formation is measured without characterisation of the products. The Vmax in the rat ovary using [1 beta, 2 beta-3H]-A4 as a substrate is 13.7 pmol/h/mg compared to 2.9 pmol/h/mg when [1 beta-3H]-A4 is used. In the human placenta, the Vmax is similar using either [1 beta, 2 betat-3H]-A4 or [1 beta-3H]-A4 (1.21 and 1.27 nmol/h/mg, respectively). Consistent results are obtained for the human placenta using either the single step chromatographic product isolation method or the tritiated water method. However, in the rat ovary the more suitable method of the two used to measure the aromatase activity is the tritiated water method employing [1 beta-3H]-A4 as a substrate. Aromatase activity in the rat ovary during estrus cycle was measured using the tritiated water method employing [1 beta-3H]-A4 as a substrate. A peak of aromatase activity at proestrus was seen which returned rapidly to its basal level at estrus. Plasma estradiol concentrations were in parallel with the aromatase activity.     

Changes in serum concentration and ovarian content of 5 alpha-androstane-3 alpha,17 beta-diol in the female rat approaching first ovulation

Concentrations of 5 alpha-androstane-3 alpha,17 beta-diol (3 alpha-diol) in serum were estimated in rats bled once during a 10-day period preceding first ovulation; ovarian contents of 3 alpha-diol were estimated over the same period. Serum values of 3 alpha-diol, measured at 1100 h, showed a significant decrease towards first ovulation; there was good correlation (r = 0.78; n = 10) between mean serum and ovarian concentrations. In 33-day-old rats no significant difference was found in serum concentrations measured at either 1100 or at 1500 h. However at first proestrus, significantly elevated serum and ovarian concentrations of 3 alpha-diol were found between 1400 and 2100 h as compared to those at 1100 h. A similar pattern was seen on the afternoon of second proestrus. On the days following first ovulation, serum and ovarian concentrations of 3 alpha-diol were comparable to those during the days preceding this ovulation. The prepubertal decrease in 3 alpha-diol production is discussed in relation to concomitant changes in secretion of estradiol and luteinizing hormone. It is concluded that, in view of the preovulatory resynthesis of considerable amounts of 3 alpha-diol, it is inappropriate to view loss of biosynthetic capacity for 3 alpha-diol as a key event in the onset of puberty.     

Modification of the ovarian cycle, ovulation and reproduction in rat by administration of p-chlorophenylalanine in the pre and post ovulation period (author's transl)]

The effect of p-Chlorophenylalanine (PCPA) administered in pre and post-ovulation phases on ovulation reproduction and ovarian cycle was studied in rats. Vaginal smears, number of ovules, mature follicles and ovaric histologic features were evaluated. PCPA administered in the periods after follicular rupture prolongs the diestrus phase from 2 to 10 consecutive days and totally inhibits the reproductive conduct. When administered in the periods just prior to follicular rupture, PCPA prolongs the estrus phase from 2 to 4 consecutive days and does not totally inhibit reproduction. A progressive increase in reproduction took place as treatment time approached ovulation, to such an extent that the number of inseminated and fertilized rats when treated at the ninth hour of the proestrus phase, was superior to the control group. PCPA administered in periods after and before follicular rupture totally inhibits ovulation in all cases. Ovaries present many mature follicles, as many as in the controls sacrificed at the 18 hour of the proestrus, just before ovulation.     

Determination of ovulation time in bitches based on teasing, vaginal cytology, and elisa for progesterone

The estrous cycle of 16 mature mongrel female dogs was monitored to evaluate the accuracy of teasing, vaginal cytology and quantitative ELISA progesterone assay to determine ovulation. The dogs were presented to male, and blood samples and vaginal swabs were taken daily during proestrus and estrus. Selected serum samples collected during estrus were assayed for endogenous LH by radioimmunoassay (RIA). Plasma samples collected during proestrus and estrus were assayed for progesterone with a commercially avialable ELISA kit. Ovulation was considered to take place 48 h after the preovulatory LH peak. Vaginal cytology smears were stained with Wright's stain and evaluated for the percentage of superficial squamous cells. Day 1 of diestrus (Day 1) was defined as a drop of 20% or more in the total number of superficial cells. Two standard curves (linear and best fitted curves) commonly used with ELISA were compared together and with the RIA progesterone assay. Ovulation was estimated to occur when progesterone concentration was 4.9 +/- 1.0ng/ml (mean +/- SD, n = 15), with a range of 3.4 to 6.6 ng/ml. Based on vaginal cytology, ovulation took place 6.9 +/- 1.6 d (n = 15) after 80% of the squamous cells were superficial and 6.8 +/- 1.4 d (n = 16) before Day 1. Ovulation took place 2.1 +/- 3.9 d (n=11) after the first day of standing estrus and 8.8 +/- 1.5 d (n = 10) before the last day of receptivity. The two standard curves were found parallel to each other and to the RIA progesterone assay. Based on the results of the present study, ELISA progesterone assay and determination of the first day of estrus by vaginal cytology are reliable methods for predicting ovulation, whereas the last day of receptivity as determined by teasing and Day 1 as determined by vaginal cytology are reliable methods to retrospectively estimate ovulation time.     

In vivo aromatization of [3H]testosterone in high and low mating lines of Japanese quail

Japanese quail selected bidirectionally for adult mating frequency were utilized to study in vivo aromatization of testosterone (T) in relation to masculine copulatory behavior. Functionally castrated high (HM) and low mating (LM) line quail were injected with 75 microCi of [3H]T. One hour after the injection, all radioactivity recovered in telencephalic-diencephalic brain tissue was in the form of T, dihydrotestosterone (DHT), or estradiol (E2). Neither the total 3H nor the [3H]T metabolite radioactivity differed between the two genetic lines. Of all [3H]T metabolic radioactivity, [3H]E2 represented 45 +/- 6 % in the HM line and 46 +/- 6% in the LM line, indicating that the line difference in mating frequency was not due to a corresponding difference in aromatase activity. Inasmuch as both the HM and LM line birds actively converted T to E2, these results implicate a neural mechanism involving E2-receptor interactions as the cause of the behavioral differences between the HM and LM lines.     

Serotonin neuroleptics change patterns of preovulatory secretion of luteinizing hormone in rats

Serotonin receptor agonists or antagonists were used in this study to determine the timing and influence of serotonergic neurotransmission on phasic secretion of luteinizing hormone (LH). Daily injections of cyproheptadine (CP) or methysergide (MS), serotonin antagonists, initiated at 1600h on the day of vaginal proestrus, blocked the LH surge and ovulation. Vaginal smears remained cornified for 2–3 days. The drugs were ineffective when given at 0800h, though they terminated the LH surge prematurely when administered at 1730h. When quipazine, a serotonin receptor agonist was injected at 1400h or 2000h on proestrus, serum LH levels rose. This effect caused the LH surge to begin prematurely or to be sustained unusually long. Quipazine injected on diestrus 2 did not cause LH levels to rise, suggesting that its effect is estrogen dependent. Serotonin turnover in the hypothalamus was greater during onset of the LH surge than during its termination. When the LH surge was prolonged by exposing rats to light on proestrous evening, serotonin turnover remained high. The results of this study indicate that phasic secretion of LH on proestrus is accompanied by and may be dependent upon a period of serotonin neural activity.     

Effect of ketoconazole on human ovarian C17,20-desmolase and aromatase

Ketoconazole, an imidazole antimycotic drug, inhibits steroid biosynthesis in adrenal and testicular tissue by blocking cytochrome P-450 dependent enzymes. To study the effect of ketoconazole on steroid biosynthesis in the human ovary we incubated human ovarian tissue (mainly theca cells) or granulosa cells with radiolabeled precursors and increasing concentrations of ketoconazole. After incubation, steroids were extracted and separated by thin layer chromatography (TLC). Activity of C17,20-desmolase and aromatase was estimated by measuring the amount of their radioactive products with liquid scintillation counting. After incubation of ovarian tissue with [3H]17-hydroxyprogesterone the production of [3H]androstenedione was reduced by increasing concentrations of ketoconazole (0-200 microM) to a minimum of 31% of basal production. This indicates a strong inhibition of ovarian C17,20-desmolase by ketoconazole with a 50% inhibiting concentration (IC50) of 23 microM. After incubation of human granulosa cells with ketoconazole (0-2000 microM) and [3H]androstenedione the production of [3H]estrone and [3H]estradiol was suppressed to minimally 37 and 35% of basal values, indicating a significant inhibition of ovarian aromatase. IC50-values were 105 microM ketoconazole for estradiol and 130 microM for estrone. In conclusion, ketoconazole was shown to inhibit human ovarian C17,20-desmolase and aromatase in vitro. As in human adrenals and testes ovarian C17,20-desmolase seems to be most sensitive to the inhibitory effect of ketoconazole.     

Effect of cycloheximide [correction of cyclohexamide] injected at proestrus on ovarian protein synthesis, peptide and steroid hormone levels, and ovulation in the hamster

Injecting 2 or 4 mg of cycloheximide (cyclo) at the onset of the proestrous release of gonadotropins prolongs the estrogen (E2) surge, diminishes progesterone (P4) secretion, and prevents ovulation by 0900 h of the next morning (Saidapur and Greenwald, 1981). The present study was designed to determine the effects of 0, 2, 4, or 8 mg cyclo injected at 1400 h proestrus (Day 4) on ovarian protein synthesis and other parameters. Ovulation was delayed until 1400 h estrus by 2 mg cyclo or prevented by 8 mg, and the latter treatment resulted in the death of all animals by 48 h. After 4 mg cyclo, ovulation was delayed in some animals, but the most characteristic feature was the development of large cystic follicles that ultimately transformed into corpora hemorrhagica. All animals lived after the injection of 4 mg cyclo. Ovaries collected 2, 8, 16, or 24 h after treatment were incubated with [3H]leucine for 1 h to assess the effects of cyclo on protein synthesis. Injection of phenobarbital at 1300 h proestrus, which blocks follicle-stimulating hormone (FSH) and luteinizing hormone (LH) surges, reduced ovarian protein synthesis at 1600 h to 61% of the control value. The incorporation of [3H]leucine was reduced to 75%, 37%, and 35% of the 1600-h control value by 2, 4, and 8 mg cyclo, respectively, but without affecting surge levels of FSH and LH. However, by 0600 h estrus, protein synthesis was increased significantly in all the cyclo-treated groups, which provides insight into the half-life of the compound (approximately equal to 8 h for 2-4 mg cyclo). At 1600 and 2200 h proestrus cyclo resulted in serum FSH and LH levels similar to controls, but increased serum prolactin and prolonged E2 levels at Day 4 of 2200 h and decreased serum P4 at both times. The second surge in FSH, which is in progress by 0600 h estrus, was abolished by 4 or 8 mg cyclo but not by the 2-mg dose. This is the first time for any species that ovarian protein synthesis has been measured in the proestrous normal or cyclo-treated animal. We conclude for the hamster that 4 mg cyclo is the optimal dose for blocking ovarian protein synthesis and ovulation and inducing formation of cystic follicles.     

Catecholamines in sow graafian follicles at proestrus and at diestrus

Endogenous dopamine, noradrenaline, and adrenaline were detected in the sow graafian follicular wall and in the follicular fluid. Noradrenaline represented the highest level and adrenaline the lowest. Dopamine and noradrenaline concentrations found in the follicular fluid were lower at early proestrus than at mid-diestrus, whereas adrenaline levels in the fluid did not differ at either stage of the estrous cycle. The sow follicular wall contained less dopamine, noradrenaline and adrenaline at early proestrus than at mid-diestrus. Concomitantly, a decrement of [3H]-dopamine and [3H]-noradrenaline uptake, and of dopamine-beta-hydroxylase activity was detected at early proestrus compared to levels detected at mid-diestrus. The findings in sow graafian follicles show the existence of relationships between hormonal status, dopamine, noradrenaline and adrenaline endogenous levels and uptake, and dopamine-beta-hydroxylase activity. Possible links between estradiol, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) levels during the pig estrous cycle and ovarian catecholamines are discussed, as is a plausible involvement of these neurotransmitters in the contractile activity of the theca layer and the processes of follicular rupture and ovulation.     

Decrease in ovarian platelet-activating factor during ovulation in the gonadotropin-primed immature rat

Platelet-activating factor (PAF) is a biologically active phospholipid that is released locally during acute inflammatory reactions and tissue injury. Since there is evidence that the biochemical events of mammalian ovulation resemble an inflammatory reaction, the objective of this study was to determine whether ovarian levels of PAF change during ovulation. At 2-h intervals during the ovulatory process in gonadotropin-primed 25-day-old Wistar rats, the ovaries were extirpated, homogenized, and extracted for lipids. The extracts were subjected to thin-layer chromatography (TLC), and the portion of the silica gel that comigrated with PAF was re-extracted and assayed for PAF activity. The PAF was measured (in fmole equivalents of synthetic PAF) by a bioassay based on the capacity of aliquots of the extracts to release [3H]-serotonin from platelets isolated from whole blood of rabbits and prelabeled with [3H]-serotonin. The ovarian level of PAF decreased (p less than 0.01) by 36% from 6.67 +/- 0.77 to 4.27 +/- 0.45 fmoles/mg ovary by 2 h after treatment with human chorionic gonadotropin (hCG), and it declined another 14% by 4 h after hCG. The ovarian PAF remained at this reduced level for up to 24 h after hCG. The administration of indomethacin (5 mg/rat, s.c.) or epostane (5 mg/rat, s.c.) at 1 h after hCG prevented ovulation, but neither drug affected the decline in ovarian PAF. Preliminary tests showed that the lipid extracts from the ovaries also contained PAF inhibitor(s) that comigrated with PAF on the TLC plates. Similar to PAF, the lipid-soluble inhibitor(s) decreased (p less than 0.05) in the ovaries within 4 h after hCG treatment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Inhibition of ovarian aromatase by prolactin in vivo

Ovarian aromatase activity was inhibited by prolactin treatment in both cycling rats and immature gonadotropin-primed animals. Cycling rats were injected s.c. with prolactin (4 mg/kg BW) beginning on diestrus 1. Aromatase activity in the largest follicles on diestrus 2 and on proestrus was reduced relative to controls. None of the prolactin-treated animals had ovulated when examined on the expected estrus morning. In other experiments, the immature pregnant mare's serum gonadotropin (PMSG)-primed rat was used as a model for the cycling rat. Microsomal aromatase activity but not the activity of the C17-21 lyase was reduced in ovaries of animals injected with prolactin [6 IU (200 micrograms)/rat] 48 h after PMSG administration and sacrificed 4 h later. Furthermore, aromatase activity was significantly increased when endogenous prolactin was inhibited by bromocryptine (CB-154). The effect of LH treatment, on the other hand, was to increase both aromatase and lyase activities. However, prolactin pretreatment did not consistently prevent the LH-induced increase in aromatase activity. The results suggest that inhibition of ovulation by prolactin is mediated, at least in part, by direct inhibition of aromatase activity.     

Pseudoaromatase in circulating lymphocytes

A variety of data suggesting a relationship between estrogens and the immune system prompted a study of aromatase activity in blood lymphocytes. A tritiated water aromatase assay detected activity of 1.9 to 25.1 pmol/g protein/h in 14 samples of human lymphocytes. To confirm these results, additional tritiated water and product isolation assays were performed on a large pool of lymphocytes obtained from 4 U of blood. An assay using [1β-³H]androstenedione generated high apparent aromatase activity, 943 pmol/g protein/h, but this activity could not be blocked by the aromatase inhibitor, CGS 16949A. More direct methods of evaluation yielded the following results: (1) PCR demonstrated no aromatase mRNA production in lymphocytes; (2) direct product isolation using [1,2,6,7-³H]androstenedione yielded insignificant production of estrone and estradiol; (3) immunostaining of fixed lymphocyte smears with a polyclonal antibody to aromatase yielded equivocal results. These data suggest the presence of pseudoaromatase in blood lymphocytes. Since circulating lymphocyte pseudoaromatase levels can be correlated with various factors in patients, such as age, menopausal status, and glucose ingestion, further studies of this activity are warranted.     

The effect of tumor necrosis factor/cachectin on follicle-stimulating hormone-induced aromatase activity in cultured rat granulosa cells

We investigated the effects of tumor necrosis factor (TNF)/cachectin on follicle-stimulating hormone (FSH)-induced aromatase activity in cultured rat granulosa cells using the stereospecific transfer of 3H from [1 beta-3H] androstenedione into 3H2O. TNF (10 pg/ml-10 ng/ml) inhibited FSH (250 ng/ml)-induced aromatase activity in a concentration-dependent manner, and 10 ng/ml of TNF completely abolished the FSH-induced aromatase activity. A time course analysis of the effects of TNF showed that TNF had no effect on induced aromatase activity, but inhibited the further induction of the enzyme by FSH. TNF (10 ng/ml) also inhibited the ability of TGF beta (1 ng/ml) to enhance aromatase activity and increase progesterone synthesis. Thus, TNF is a component of the complex array of proteins that modulate ovarian function and, as such, may play a physiological role in the regulation of the granulosa cell. In view of its association with cachexia, it may also play a pathophysiological role in the suppression of reproductive function during chronic illness.     

Qualitative and quantitative data on experimental luteinization in the female rat

The dose-effect of 1.5-16 mcg luteinizing hormone (LH) per 100 gm body weight injected in rats at 1100-1200 on proestrus was compared with 30 mg meprobamate given to controls at the same time, on luteinization and ovulation seen in serial ovarian sections. The WII Wistar rats were killed. Luteinization with or without ovulation increased with dose (1.5, 3, 5, 8, and 16 mcg) of LH to a plateau (90%) above the 5 mcg dose, compared with 18% in controls. 2-5 animals in each dose group had preluteinized follicles, characterized by a dissociation of the cumulus oophorus from the granulosa. The absolute frequency of ovulation increased linearly with LH dose, but the frequency of ovulation among rats that luteinized was invariant. The coefficient of ovulation, calculated as the mean incidence of ovulation in relation to the total number of luteinized or preluteinized follicles in each rat, decreased from .769 in controls to .580 in the 3 mcg group, then rose to .916 in the 16 mcg group. Thus, in proestrous rats, low doses of LH induce corpora lutea with retained ova. The threshold dose of LH for luteinization and for ovulation is lower in proestrus than in diestrus II, but varies slightly in different strains of rats.     

The hypothalamic levels of the endocannabinoid, anandamide, peak immediately before the onset of puberty in female rats

Several data suggest that the endogenous cannabinoid system plays a role in neuroendocrine regulation in adult individuals, although the information on its involvement in peri-pubertal processes is scarce. In the present study, we have examined the ontogeny (from postnatal day [PND] 5 up to adulthood) of hypothalamic and anterior pituitary contents of anandamide (arachidonyl-ethanolamide, AEA). We observed that the content of AEA in the hypothalamus was low at PND5, PND15 and PND25, but it markedly increased (approximately 3-fold) immediately before the puberty (on the day of 1st proestrus), to return to intermediate values immediately after the vaginal opening (day of 2nd proestrus) and, eventually, adulthood. By contrast, no consistent differences were observed in AEA levels in the anterior pituitary. These results demonstrate the occurrence of a parallelism between the peri-pubertal events and a rise in the hypothalamic content of AEA immediately before the puberty, which might indicate that this endocannabinoid may be involved in the onset of puberty in rats.